ScienceNow: Astronomers today reported the discovery of a planet beyond our solar system that's just twice the diameter of Earth. But this new neighbor is far from habitable: CoRoT-Exo-7b is either a hellish world of erupting volcanoes and sizzling temperatures, or it's covered by a scalding ocean. Either way, the discovery could pave the way toward finding more Earth-sized alien worlds, some of which may actually be habitable.